Jackson's Knowledge Argument

PHIL 205 – Paper #2

Jackson’s Knowledge Argument and the Best Physicalist Response

Frank Jackson uses the knowledge argument in an attempt to prove that physicalism is false. Physicalism views the world purely by its physical aspects so there is a special consequence of physicalism that arises, which states that if we know all the physical information then we know all there is to know. With his knowledge argument, Jackson attempts to disprove this notion by arguing that physicalism fails to account for the qualia or the sensation of what it is like to be in a certain mental state; so to know everything physical about an experience does not mean you know everything about that experience. Jackson provides the case of Fred, who is physically identical to human beings, the exception being a highly developed optical mechanism. While normal human beings can only see the color red, Fred can distinguish further and see two different colors, namely red1 and red2. A further analysis of his brain shows that his optical system is able to differentiate between two different wavelengths in the red spectrum just as our brain differentiates between the wavelength of green and blue. Therefore for Fred, red1 and red2 are two different colors.

Using the premise of Fred, Jackson argues that no amount of physical information provided about Fred can tell us what the experience of seeing red1 and red2 is like; it cannot explain how these new colors are different. For example, we can know all the physical processes that occur in Fred’s optical system when he sees red1 and red2; perhaps he has extra cones or his cones react differently to red light than ours. We can know all the physical properties about Fred including his body, internal physiology, and behaviors, but we cannot know what it is like for Fred to experience the difference between red1 and red2. So, if physicalism was true, knowing all the physical properties about Fred would entail that we know all there is to know...